INCREDIBLE footage has shown fighter jets, choppers and tanks taking part in US-led war games simulating a North Korean invasion.
Joint exercises with South Korean allies saw the Americans deploy a nuclear-powered submarine as Pyongyang warned of an "inevitable" response.
South Korean President Yoon Suk-yeol personally oversaw the finale of the "annihilation" exercises, involving over 2,500 troops and 610 "state-of-the-art weapons" yesterday.
Videos of the drills show jets swooping at high speeds while firing live rounds over the Seungjing Firing Range in Pocheon, near the Korean border.
Choppers and tanks then roll in to participate in the practice, which is designed to mimic an invasion from the North.
Speaking at the event, Mr Yoon said: "Protecting our national security by ourselves is the real peace.
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"Only a powerful army that foes would not dare overcome and an army that can win against enemies can guarantee the freedom, peace and prosperity of South Korea."
However, the exercises prompted a furious reaction from Pyongyang.
The country's defence ministry said in a statement: "Our response to this is inevitable.
"Our armed forces will fully counter any form of demonstrative moves and provocation of the enemies."
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It comes as northern forces were accused of violating the demilitarised zone between the nations "under the pretext of controlling crab-catching fishing boats in the Yellow Sea".
Meanwhile, the North fired off two short-range ballistic missiles into the sea as tensions mount in the wake of a summit between Mr Yoon and President Biden.
The US leader took a firm line, warning that any nuclear attack on the US or its allies from North Korea would result in the end of the regime that launched it.
The Americans also agreed to ramp up their strategic assets in the South.